12th Biology Practical ~ (Part B) 5. Study of V.S. ovule through permanent slide/relevant chart

12th Biology practical book answers pdf Maharashtra board 

~Study of V.S. ovule through permanent slide/relevant chart

Ovule (megasporangium) is enclosed in the ovary. There may be one or many ovules in an ovary.

Aim: Study of anatropous ovule and functions of its various parts.

• The ovule in which micropyle, chalaza and funicle are not in one straight line and integuments run parallel to funicle is called as anatropous ovule. It is also called as inverted ovule and is the most common type of ovule, in angiosperms.
• The ovule shows two main parts as: - body and funicle.
• The body shows two integuments originating from base of ovule reaching up to the tip of ovule. The tip shows a small cleft, left by two integuments called as micropyle. The integuments enclose a mass of fertile, parenchymatous, diploid cells called nucellus. There is only one fertile cell located more or less in the centre of nucellus but towards micropylar end of ovule, this is called megaspore mother cell. It finally develops into only one female gametophyte (embryo sac).
• In monosporic embryo sac, the female gametophyte. It is 8-nucleated and 7-celled structure
• Female gametophyte consists of egg apparatus, 2-polar nuclei and 3-antipodal cells.
• The egg apparatus is located closer to the micropylar end of embryo sac. It consists of central haploid egg cell and 2 supporting laterally placed haploid synergids.

·         In mature female gametophyte, the 2 polar nuclei fuse to form the diploid secondary nucleus (definitive nucleus).

 

Comment on the special features of anatropous ovule and embryo sac:

1. Anatropous ovule:

The ovule which has downwardly directed, micropyle is called anatropous ovule. Micropyle, chalaza and funicle are not in one straight line and integument run parallel to funicle.

It is also called as inverted ovule. It is one of the most common types of ovules in angiosperms.

 

 2. Embryo sac:

It is the female gametophyte. It is eight nucleated and seven celled structures.

It consists of egg apparatus, 2 polar nuclei and three antipodal cells.

Egg apparatus is located towards micropylar end of embryo laterally placed synergid.

 

 

Questions

1. What is ovule?

The egg containing body present within ovary is known ovule.

 

2. Enlist the functions of micropyle prior to fertilization and after fertilization in the ovule of angiosperms.

Micropyle gives passage for the entry of pollen to be during fertilization.

 

3. What is the double fertilization?

Out of two male gametes produced by the male gametophyte in. angiosperms, one fuses with female gamete (egg) and the other with secondary nucleus.

Thus, both male gametes take part in fertilization and fertilization occurs twice. It is called double fertilization.

 

4. Give functions of:

a. Integuments

Give protection to inner contents of ovule.

 

b. Nucellus

Produces integument toward chalaza end.

Produces embryo sac toward micropylar end

 

c. Funicle

Give support to body of ovule

Supplies food material to body of ovule from placenta.

 

d. Synergid cells

One synergid gives site for entry of male gamete into embargo

Other synergid is nutritive in function.

 

e. Antipodal cells

Nutritive in function.

 

5. Distinguish between female and male gametophytes in angiosperms.

 

Female gametophytes	Male gametophytes
1) Megaspore produces female gametophyte	1) Microspore produces male gametophyte
2) Female gametophyte produces female gamete	2) Male gametophyte produces male gamete
3) Female gametophyte has a single phase of growth	3) Male gametophyte has two phases of growth

Fin :)